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Some Bizarre Black Holes Put On Light Shows

By Rae Ellen Bichell | NPR
Wednesday, January 11, 2017

People think of black holes as nightmare vacuum cleaners, sucking in everything in reach, from light to stars to Matthew McConaughey in the movie Interstellar. But, in real life, black holes don't consume everything that they draw in.

"They're actually pretty picky eaters," says Jedidah Isler, an astrophysicist at Vanderbilt University. She spends most days chipping away at one of the universe's biggest mysteries: How do the huge, overactive black holes, known as quasars, work?

"They are billions of times the mass of our own sun," she says. "I like to call them 'hyperactive,' in the sense that they are just taking on a lot more than an average black hole."

And these monster black holes tend to do something strange. They not only reject material, but they use it to put on a space version of a fireworks show, shooting out shredded stars and other things in a stream of light and charged particles.

"Think of them as cosmic water hoses that are spewing out all kinds of particles and light," says Isler.

These are some of the most powerful particle streams ever observed, causing chaos in their host galaxies. Theoretically speaking, if an unlucky planet happened to cross paths with one of those jets, Isler says, it would not be pretty.

"It would basically destroy the planet completely. It would completely eviscerate anything that got in its way," she says. She added, "You know, things are being eviscerated in space all the time. It's part of what makes it fun."

Isler specializes in the subset of quasars that happen to have their jet streams of material pointed toward Earth. These are called blazars, or "blazing quasars."

Telescopes built in the last decade, like NASA's Fermi Gamma-ray Space Telescope, have spotted a few thousand blazars. But don't panic.

"Thankfully, they are far enough away that they are not going to have any negative impact on us as human beings," Isler says. One of the closest blazars is 2.5 billion light-years away. "But they do serve as really interesting laboratories to understand these really exotic systems," she says.

"They are able to accelerate particles to 99.99 percent of the speed of light," Isler says. "How does that happen? So, I'm interested in where along that jet do we get this acceleration, and what is the physical mechanism that is responsible for the acceleration of particles that we see?"

By analyzing data from a large sample of blazars, she and her colleagues have found that some particles exhibit high-energy acceleration closer to the black hole than expected, suggesting that differences in blazar jets occur because of an internal process, like turbulence, as opposed to a more consistent factor, like how quickly the blazars draw in material.

If the scientists can figure out how these natural particle accelerators work, they may begin to understand the physical laws that guide these unusual black holes, and maybe a lot of other systems out there that are capable of pulling things in and flinging them out.

"That process happens at many different scales across the universe with many different systems," Isler says. For example, when planets form, they pull nearby material into what are called protoplanetary disks. Sometimes, they shoot that material out in jets, too, though on a much smaller, weaker scale than blazars do.

"There may be some way that this process is universal in our cosmos," she adds. Understanding supermassive, hyperactive black holes could be a first step in figuring that out.

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